JP3356603B2 - Charging device and image forming apparatus incorporating the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for uniformly charging a photosensitive member via a voltage applied to the charging roller while a charging roller is in contact with the photosensitive member, and an image forming apparatus incorporating the charging device. The present invention relates to an invention applied as an apparatus, and more particularly to an invention relating to a charging device incorporated in a copier, a printer, a facsimile, or a process cartridge of these devices, and an image forming apparatus incorporating the device.

[0002]

2. Description of the Related Art Conventionally, respective process means of exposure, development, transfer, cleaning (removal of residual toner), charge elimination and charging are arranged on the outer peripheral surface of a photosensitive drum, and an image is formed by a predetermined electrophotographic process. Electrophotographic apparatuses based on the so-called Carlson process are well known.

The charging means used in this type of apparatus is generally a corotron type in which a high voltage is applied to a thin tungsten wire to perform corona discharge, or a charging means in which a voltage of several hundred volts is applied to a conductive roller to contact and charge a photosensitive drum. (Japanese Unexamined Patent Publication No. 5-297690, etc.), a device in which a voltage is applied to a conductive brush to charge while contacting a photosensitive drum, and a group of magnetic particles is attached to a conductive sleeve in which a magnet is inserted. A so-called particle charging method has also been proposed in which a brush-like magnetic spike is rubbed against a photoreceptor drum and a charging bias is applied to a group of magnetic particles via a sleeve to perform charging (Japanese Patent Laid-Open No. 59-133569 and others). ).

However, the corotron method uses a high voltage, generates ozone, and has many safety and environmental problems. The method using a charged brush or charged particles requires a long period of time due to brush abrasion and particle deterioration. Therefore, it is difficult to uniformly charge the photosensitive member. Therefore, in a state where the charging roller is in contact with the photoconductor, charging is performed while applying a charging bias to the photoconductor drum via the charging roller.
A so-called charging roller system has attracted attention. On the other hand, when the charging roller is rotated at the charging position of the photoconductor while contacting, the cleaning blade is rubbed off, and high-resistance foreign substances such as silica, toner, and polyvinylidene fluoride used as a lubricant of the cleaning blade are removed. When these high-resistance foreign substances adhere to the charging roller and adhere to the peripheral surface (charging surface) of the charging roller, poor charging occurs at that portion, and image defects such as vertical stripes occur. In addition, if low-resistance foreign matter such as paper powder rubbing through the cleaning blade adheres to the peripheral surface (charging surface) of the charging roller, it may cause abnormal discharge under high humidity and image deletion.

[0005] Further, if these foreign matters remain adhered for a long period of time, the charging member and the drum surface will be damaged over time, causing streak-like image defects. For this reason, in a charging device using the charging roller, a charging cleaning member for removing silica, paper dust, and the like adhering to the surface of the charging roller is disposed in contact therewith.

[0006] The charging cleaning member is formed in a blade shape or a roller shape. However, the charging cleaning member is configured to perform cleaning while being in contact with the charging roller on the side opposite to the nip position with the photosensitive drum. In some cases, the cleaning member and the charging roller may make uneven contact in the axial direction due to roller run-out or poor straightness. For this reason, the roller member is formed of a sponge roller, and the sponge roller is
There is disclosed a technology that is driven to rotate. (JP-A-5-297690)

[0007]

In such prior art, however, the charging roller that rotates the sponge roller following rotation is connected to the photosensitive drum via a transmission gear.
In order to adopt a configuration in which the sponge roller is configured to be driven to rotate in contact with the charging roller and to rotate in synchronization with each other, a braking action occurs in a direction in which the sponge roller inhibits rotation of the charging roller. The driving force and the braking force from the sponge roller side cause chattering of the rotation of the charging roller, that is, a minute vibration, and the adhesion at the nip position is reduced, making uniform charging difficult.

In particular, when the charging bias voltage applied to the charging roller is an alternating voltage, the charging is performed by forming an oscillating electric field in the air in the space between the charging roller and the photosensitive drum. The close contact state at the nip position between the charging roller and the photosensitive drum does not cause much problem. However, when a DC charging bias is applied, the charging current flows to the photosensitive member via the nip formed between the roller and the drum. Due to the configuration, the adhesion of the roller to the drum side is strongly required, and the decrease in the adhesion makes uniform charging more difficult. In addition, due to the braking action in which the sponge roller is urged, a peripheral speed difference occurs between the charging roller and the photosensitive drum, and particularly when the photosensitive drum is formed of a soft OPC drum, scratches occur on the surface of the drum. Smooth image formation becomes impossible.

[0009] In view of the drawbacks of the prior art, the present invention has
It is an object of the present invention to provide a charging device capable of stably performing cleaning of a charging roller for a long period of time and an image forming apparatus incorporating the charging device. It is another object of the present invention to provide an image forming apparatus capable of stably and uniformly charging for a long period of time even when a DC charging bias is used.

[0010]

The present invention is applied to a charging device using a cleaning roller member as cleaning means for cleaning a charging roller, wherein the cleaning roller member is constituted by a sponge-like elastic roller . The sponge-like elastic roller is driven to rotate in a direction of forward feed rotation at a contact position with the charging roller, and the peripheral speed of the sponge-like elastic roller at the contact position is larger than the peripheral speed of the charging roller by driving the photoconductor. Set the rotation speed of the sponge-like elastic roller so that
The sponge-like elastic roller and the charging roller are controlled so that the distance between them is constant, and furthermore, the charging roller shaft is movable and biases toward the center of the photosensitive drum axis, whereby the charging roller and the sponge-like roller are pressed. The dynamic friction coefficient between the elastic rollers is set smaller than the dynamic friction coefficient between the charging roller and the photosensitive drum. 4. The charging roller as claimed in claim 3, wherein the charging roller is disposed in contact with the photosensitive member which is driven and rotated, and a sponge-like roller member which contacts the charged surface of the charging roller to clean the charged surface. With
In the image forming apparatus, the sponge-shaped roller is moved in the direction of forward feed rotation at a contact position with the charging roller .
The roller member is driven and rotated, and the roller at the contact position is further rotated .
The sponge-like rollers the charging roller rotation speed set of the sponge roller member so as to be larger than the peripheral speed of the peripheral speed charging roller member by a driven rotating the photosensitive member, the spot
The diameter of Nji shaped roller member to slightly larger than the diameter of the charging roller 4, the sponge roller member, the number of cells of about 1
A sponge material of 0 to 60 pieces / inch, a photoreceptor is an OPC photoreceptor drum, a charging roller is provided with a rubber layer on a surface layer, and a rubber hardness of the surface layer side is 30 to 50 degrees by Asker-C measurement. with each constitute dynamic friction coefficient between the charging roller and the cleaning roller is set to smaller than the dynamic friction coefficient between the charging roller and the photosensitive drum. In this case, the charging roller is added with a conductive component and has a resistivity of 10 ⁷ Ω · c.
m, the surface of the polyurethane rubber is preferably polished to set the surface roughness of the roller after resin coating to Rz <7 μm. According to this configuration, since the cleaning roller member is an elastic roller, a sufficient nip can be ensured between the cleaning roller member and the charging roller even if the charging roller deflects or has a poor straightness.

Since the elastic roller performs forward feed rotation in a direction to promote the rotation of the charging roller, smooth cleaning can be performed while rubbing the charging roller without causing a braking action. In this case, the elastic roller performs forward rotation so as to rotate stably without causing a braking action to the charging roller and applying unnecessary urging force to the charging roller. Since the roller performs a sliding action with a slight difference in peripheral speed and does not apply unnecessary urging force to the charging roller and guarantees synchronous rotation of the photosensitive member and the charging roller, if the peripheral speed ratio is too large, Synchronous rotation with the photoconductor cannot be guaranteed, and the cleaning roller is consumed.

Therefore, in the present invention, the peripheral speed ratio of the forward feed rotation is set to less than 2, preferably 1.8 or less. It is preferable to use urethane foam or other porous sponge material for the elastic roller. In order to efficiently remove extraneous matter such as toner by rubbing, the number of cells of the sponge material is about 10 to 10. Preferably it is 60 pieces / inch. In other words, if a cell having a large number of cells is used, the scraped foreign matter cannot be taken into the elastic member, and the foreign matter remaining on the surface of the elastic member is rubbed against the charging roller, causing damage to the charging roller. And the like.
On the other hand, if a cell having a small number of cells is used, similarly, not only the scraped foreign matter cannot be taken into the elastic member, but also the frictional resistance is increased and an unnecessary urging force is applied to the charging roller side. Become.

Therefore, the number of cells of the sponge material of the elastic roller is about 10 to 60 cells / inch, preferably about 20 to 60 cells.
Pcs / inch, more preferably about 30-60 pcs / inch. According to the above configuration, the skeleton of the sponge scrapes off foreign matter on the surface of the charging roller due to a difference in peripheral speed between the sponge roller and the charging roller, and stores it in a cell in the sponge to reliably remove foreign matter attached to the surface of the charging roller. It can be removed and re-adhesion to the charging roller can be prevented.

The present invention employs a configuration in which the drive of the cleaning roller is not transmitted to the charging roller, but the driving of the photosensitive member is transmitted to the charging roller, that is, the charging roller is driven to rotate relative to the photosensitive member. As a result, the urging force of the cleaning roller is generated, so that the synchronous rotation on the charging roller side can be smoothly ensured. As the means for following rotation, the shaft gear of the charging roller may be connected to the shaft gear of the photosensitive drum, or the charging roller may be configured to be rotatable and rotatable on the photosensitive drum. As described above, it is preferable that the feed roller rotates forward at the contact position while slipping occurs between the cleaning roller member and the charging roller.

In the present invention, the photoreceptor is an OPC photoreceptor drum, the charging roller is provided with a rubber layer on the surface, and the rubber hardness on the surface side is 30 to 50 degrees, preferably 40 to 50 degrees.
It is preferable that the image forming apparatus is constituted by a charging roller set in the range of degrees and the cleaning roller member is constituted by a sponge roller, and the action of the invention can be smoothly achieved without damaging the photosensitive member.

Further, by the combination of the hardness setting and the sponge roller, only the rubber hardness of the charging roller can affect the adhesion between the charging roller and the photosensitive member while minimizing the influence on the sponge roller side. This enables more accurate contact. In the case of the present invention, since the charging roller is a driven roller, and the cleaning roller is a driving roller and a sponge roller, the vibration suppressing function works more on the charging roller, and the occurrence of chatter due to the rotation of the charging roller is completely prevented. It is possible to rotate the charging roller synchronously with good tracking with the photosensitive drum,
Thus, even when the charging bias is set to the DC charging bias, the above-described effect can be smoothly achieved, and uniform charging can be stably performed over a long period of time.

The reason for setting the rubber hardness on the surface side of the charging roller is that the entire rubber layer is 30 to 50 degrees, preferably 4 degrees.
It may be in the range of 0 to 50 degrees, or even when, for example, a single conductive rubber layer is formed by changing the molecular weight distribution or the degree of cross-linking in the rubber layer radial direction, only the rubber hardness on the surface layer is in the above range. I just need.

In the present invention, the dynamic friction coefficient between the charging roller and the cleaning roller is set smaller than the dynamic friction coefficient between the charging roller and the photosensitive drum in order to guarantee the synchronous rotation between the charging roller and the photosensitive drum even when rotating forward. As a means for easily realizing such a configuration, the charging roller and the cleaning roller are held at an interval to support both roller shafts, and the charging roller shaft is centered on the photosensitive drum shaft. It is preferable that the pressure is applied to both ends of the roller shaft. Preferably, the total pressure to the photosensitive drum side is set to 250 to 600 g at the end of the charging roller shaft. Is good.

The surface of the elastic roller, especially the cleaning roller composed of a sponge roller, needs to be shaped. The shaping means includes a polishing cutting method and a hot wire cutting method. The state is different. Since the polishing cutting method is a mechanical shaping means that does not involve a thermal melting means, in other words, in order to perform shaping while microscopically shaving the surface with a polishing whetstone or the like, as shown in FIG. The surface of the cleaning roller 51 is not rounded at the tip than the surface layer of the sharp skeleton 51a.
A state in which the if-edge-shaped brush-like minute pieces 51b protrude, in other words, a cut is formed on the surface of the skeleton 51a having an acute angle. On the other hand, in the hot wire cutting method, the eyes of the sponge are crushed because the surface is shaped with the heated wire, and the cut of the skeleton also has a round surface due to heat, and the brush-like small pieces protrude from the surface layer. Absent. Therefore, in a state where the brush-like minute pieces 51b protrude from the surface layer of the sharp skeleton 51a on the surface of the cleaning roller 51, the cleaning effect is more efficiently achieved by the catching effect of the sharp skeleton 51a and the brush-like minute pieces 51b. Can be obtained,
In the hot wire cutting method, since the sponge's eyes are crushed, it is considered that the capturing effect is smaller than the former.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be illustratively described in detail with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention, but are merely illustrative examples. Not just. FIG. 1 shows a basic configuration diagram of an image forming apparatus to which the present invention is applied, in particular, a process unit around a photosensitive drum 1 of a printer.
An ED unit 8, a developing unit 60, a transfer roller 7, a cleaning blade 3, and a charge removing unit 2 including an eraser;
A charging roller 4 is disposed, and after the charge is removed by the charge removing means 2 as is well known, an exposure latent image is written by the LED unit 8 on the photosensitive drum 1 uniformly charged by the charging roller 4,
The exposure latent image is developed into a toner image by a developing unit 60 by reversal development.
After the transfer to 0, the residual toner is removed by the cleaning blade 3. The residual toner removed by the cleaning blade 3 is stored in a waste toner bottle (not shown) by a screw (not shown).

Next, the respective process means will be described. The photoconductor drum 1 uses an OPC drum 1 (organic photoconductor) having a diameter of 30φ and a negative charging polarity, and is configured to be rotatable at a predetermined peripheral speed in the direction of the arrow. The thickness (the total thickness of GGL, CTL, etc.) of the photoconductor layer of the photoconductor drum 1 is set to 25 μm, and a photoconductor having high viscoelastic properties is used for the CTL layer. It is preferable to use a defect-less photoreceptor in which the coating surface of the photoreceptor has irregularities regulated.

As is well known, the LED units 8 are
It consists of an LED head with D elements arranged and a focusing lens,
An exposure latent image corresponding to image information can be written on the photosensitive drum 1.

The developing unit 60 comprises a developing container 61 containing a multi-component developer composed of a carrier and a toner, and a developing roller 62 containing a fixed magnet assembly (not shown). A DC development bias Vg of -450 V is connected to perform development by low electric field reversal development.

The carrier is formed by fixing conductive fine particles on the surface of carrier base particles in which a magnetic substance is uniformly dispersed in a binder resin, and has a magnetic force of 5 kOe (Oersted). Is 55 to 80 emu / g and the average center particle size of the carrier is 35
A developer having a particle size distribution of 15 μm or more, particularly 35 μm or less, is used.

As the toner, an ordinary high-resistance or insulating toner is used. For example, a magnetic substance is added to a binder resin, a coloring agent, a charge controlling agent, an offset preventing agent, etc., and the average central particle size is 5 to 15 μm. An appropriate mixing ratio of the carrier and the toner is set to, for example, 85 to 90:15 to 10% by weight as the front and rear magnetic toners.

The transfer roller 7 has a resistivity of 10 ⁵ Ω · cm.
The following conductive elastic roller, specifically a urethane rubber roller, is used, and the transfer bias 70 is set to +250 V to +2000 having a polarity opposite to the surface potential of the photoconductor 1 and the polarity of the toner image charge.
Set to V.

On the other hand, the cleaning blade 3 is
1, a plate-like polyurethane elastomer material having a wedge-shaped cross section at its tip is attached to a support member (not shown), and the corner of the tip abuts on the photosensitive drum 1 almost in line contact. .

The charging roller 4 is driven and rotated in synchronism with the photosensitive drum 1 to add a conductive component to the periphery of a roller shaft 41 composed of a solid stainless steel shaft of 6φ to have a resistivity of 1
It is formed by molding a polyurethane rubber 42 of not more than 0 ⁷ Ω · cm, polishing the surface and shaping it into a 12φ roller shape, and coating the surface with a nylon resin. The roller surface roughness is set to Rz <7 μm, preferably 4 to 6 μm.

The polyurethane rubber 42 constituting the charging roller 4 has a different molecular weight distribution and a different degree of crosslinking, and the rubber hardness of the rubber layer is set in the range of 40 to 50 ° by Asker-C measurement. If the surface rubber layer is within the rubber hardness range, the surface layer of the rubber layer 42 of the charging roller 4 may be subjected to a hardening treatment if necessary. The molecular weight distribution and the degree of crosslinking may be changed in the radial direction toward the rubber surface layer.

On the back side of the charging roller 4, a cleaning roller 5 composed of a sponge roller is disposed in contact. The cleaning roller 5 is formed by covering a roller shaft 52 with a sponge layer 51 made of urethane foam in a cylindrical shape.
12.5φ slightly larger than the diameter of the charging roller 4
Is set to Note that the surface shaping of the cleaning roller 5 is performed by a polishing cutting method, and a state in which the brush-like minute pieces 51b protrude from the surface layer of the sharp skeleton 51a as shown in FIG. The cuts are formed in a flickering shape (as if implanted) on the surface of the acute-angled skeleton 51a.

As shown in FIG. 1, the surroundings of the cleaning roller 5 and the charging roller 4 on the back side thereof are disposed around the collection container 4.
0, and the cleaning roller 5 is rotated with a peripheral speed difference, whereby the skeleton of the urethane foam sponge scrapes foreign substances on the surface of the charging roller 4 by the peripheral speed difference between the sponge roller 5 and the charging roller 4, and removes it. By storing the foreign matter in the cells in the sponge, foreign substances adhering to the surface of the charging roller 4 can be reliably removed.

FIG. 4 shows a configuration of a bias circuit for performing the charging and development. Reference numeral 30 denotes a high-voltage power supply circuit for supplying a DC voltage V of 1200 V to the voltage adjustment circuit, and 31 denotes a voltage adjustment circuit. charging bias voltage and the developing bias voltage assembly adjustment Boriyu for adjusting the - arm and user adjustment Boriyu - comprises a beam, the Boriyu - the roller shaft of the charging roller 4 via the correcting resistor is adjusted charging bias V _t by arm The developing bias is applied to the developing roller 62. In this case, the charging bias is configured such that a DC voltage of -800 to -1000 V is applied to the charging roller 4 and a charging current of about 3 to 6 µm flows. The developing bias is -3.
A DC voltage of 50 to -450 V is applied to the charging roller 4 so that a developing current of about 170 to 173 μm flows.

[0033] Figure 3 shows the configuration of the charging roller 4 around the drive system, after transmitted to the shaft gear 1A of the photosensitive drum 4 from the gears M ₁ of the motor M through the relay gear 59, shaft gear 1A A gear 1A of the charging roller 1 is meshed with the charging roller 1 so that the charging roller 4 is driven by the rotation of the photosensitive drum 1 and rotates synchronously. The gears 5A of the cleaning roller 5 meshes with gears M ₁ of the motor M through the relay gears 58, 58.

In this case, the cleaning roller 5
The number of gears is set so that the rotation direction of the roller is in the forward direction with respect to the charging roller 4 at the contact position with the charging roller 4, and the peripheral speed between the cleaning roller 5 and the charging roller 4 is varied. Relative peripheral speed difference is 1.0 ~
2, preferably set in the range of 1.1 to 1.5. Therefore, in order for the cleaning roller 5 to rotate forward with respect to the charging roller 4, that is, to set the charging roller 4 in a counterclockwise rotation direction with respect to the clockwise direction, the two relay gears 58, 58 are interposed, and the diameter ratio is adjusted. By adjusting, the relative peripheral speed difference is set in a range of 1.1 to 1.5.

The charging roller 4 is, as shown in FIG.
The charging roller shaft 41 is fitted into a guide groove 20A recessed in the drum support frame 20, and a pressure is movably applied to both ends of the roller shaft 41 toward the center of the photosensitive drum shaft 1a using springs 49. Energize. In this embodiment, the length of the charging roller 4 is set to 226 mm, the distance from the roller end to the spring contact position is set to 7.2 mm, and the A4 size recording paper is configured to be chargeable.

On the other hand, the cleaning roller 5 and the charging roller 4 are controlled by the housing of the collection container 40 of the charging roller 4 so that the interval between them is constant. As a result, the sponge layer 51 of the cleaning roller 5 always comes into pressure contact with the charging roller 4 at a predetermined nip and the contact pressure is almost constant, so that the load applied to the charging roller 4 by the cleaning roller 5 becomes as small as possible. I have to. As a result, the load of the cleaning roller 5 is not applied to the photosensitive drum 1 and only the load of the spring 49 is used.
Is determined on the photosensitive drum 1 side.

In this embodiment, the load of the spring 49 is set so that the total pressure on the photosensitive drum side at the end of the charging roller shaft 41 is 250 to 600 g, specifically 300 g. Cleaning roller 5 and charging roller 4
The interval between them is 10-11 mm, preferably 10.5 m
m, and the amount of compression of the sponge layer 51 constituting the cleaning roller 5 is 0.5 to 1.5 mm, preferably 1 mm
Set to.

[0038]

Next, in order to confirm the effect of the present invention, while the cleaning roller 5 and the charging roller 4 are set to a forward rotation, the peripheral speed ratio is 1 (synchronous rotation with the charging roller).
Image formation was performed at a printing rate of 5% for each of 50,000 sheets (50K sheets), which were different from 1, 1.2, 1.5, 1.8, 2, and 3, respectively. A porous sponge layer 51 made of urethane foam was used for the cleaning roller 5 used in this experiment, and the number of cells on the outer peripheral surface of the sponge layer 51 was set to 50 cells / inch. It is shaped by. When examining the configuration, FIG.
As shown in FIG. 3, in the case of the peripheral speed ratio of 1 (comparative example), vertical streaks began to appear in the image from about 20,000 sheets after the image formation, and the white spot further increased until 30,000 sheets were printed. Vertical streaks occurred on 10,000 sheets or more, and when the charging roller was disassembled after printing 50,000 sheets, the charging roller was found to be damaged. The peripheral speed ratio is 1.2 to 1.
In the case of Example 8 (Example), an extremely clear image could be obtained even after printing 50,000 sheets, and when the charging roller was disassembled, the surface was extremely clean.

Further, those having a peripheral speed ratio of 2 to 3 (comparative example)
Vertical streaks began to appear in the image from about 30,000 sheets after image formation.
The white spot was further increased by 10,000 sheets of printing, and vertical streaks occurred on 40,000 or more sheets. When the charging roller was disassembled after printing 50,000 sheets, the charging roller was damaged.

Next, when the peripheral speed ratio was set to 1.5, the number of cells on the surface of the sponge layer 52 was 10, 20, 3
Using the cleaning rollers set at 0, 40, 60 / inch, and 80 / inch, images were formed on each of 50,000 sheets at a print rate of 5%.

As a result, as shown in FIG. 7, in the case of 80 / inch having a large number of cells (comparative example), a small white spot is generated after a while after exceeding 10,000 sheets, and the printing is performed more than 20,000 sheets. The vertical streaks increased so that they could be confirmed visually.
When the charging roller was disassembled after printing 50,000 sheets, the charging roller was found to be damaged. Further, in each of the examples having 40 and 60 / inch cells, an extremely clear image could be obtained even after printing 50,000 sheets, and the surface was extremely clean when the charging roller was disassembled. .

In the embodiment having 20 / inch cells, slight image disturbance occurred after printing 50,000 sheets, and when the charging roller was disassembled, foreign matter was slightly attached to the surface of the charging roller. Further, in the comparative example in which the number of cells was as small as 10, a slight vertical streak was generated from around 40,000 sheets, and after the printing of 50,000 sheets, the vertical streak was increased to be visually confirmed. When the charging roller was disassembled, scratches were found on its surface. Accordingly, the number of cells of the sponge layer 51 of the elastic roller is preferably about 20 to 60 cells / inch, preferably about 30 to 60 cells / inch, and more preferably about 40 to 60 cells / inch.

In the above state, the spring pressure of the spring 49 applied to both ends of the charging roller 4 was 200 g (Comparative Example 5), 300 g (Example 1),
When the charged state was confirmed to be different from 700 g (Comparative Example 6), charging unevenness occurred in Comparative Example 3 in which the spring pressure was 200 g, and when the spring pressure was 700 g, the voltage on both sides of the charging roller 4 became higher than the central portion. Again, uneven charging occurs in the axial direction.

[0044]

As described above, according to the present invention, the charging roller can be stably cleaned for a long period of time, and is particularly effective for an apparatus using a DC charging bias. And so on.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus applied to the present invention.

FIG. 2 shows a configuration of a drive system around a charging roller 4 of the apparatus shown in FIG.

FIG. 3 shows a fitting state of a charging roller and a photosensitive drum.

FIG. 4 shows a configuration of a bias circuit for performing charging and development of FIG.

FIG. 5 is a partially enlarged view of the cleaning roller shown in FIG. 1;

FIG. 6 is a table illustrating a relationship between a peripheral speed difference between a cleaning roller and a charging roller and a charging / image forming state.

FIG. 7 is a table showing the relationship between the number of cells on the surface of a cleaning roller and the state of charging / image formation.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum 1A photosensitive drum shaft gear 4 charging roller 4A charging roller shaft gear 5 cleaning roller 5A cleaning roller shaft gear 49 spring 51 sponge layer 51a surface layer skeleton 51b brush-like minute piece

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Yojiro Sato 704-19 Noshino, Tamaki-cho, Tamai-cho, Mie Prefecture Inside the Mie Tamaki Plant, Kyocera Corporation (56) References JP-A-6-149012 (JP, A JP-A-2-301779 (JP, A) JP-A-6-161171 (JP, A) JP-A-7-140762 (JP, A) JP-A-5-297690 (JP, A) JP-A 8- 62948 (JP, A) JP-A-6-230657 (JP, A) JP-A-5-88508 (JP, A) JP-A-4-106565 (JP, A) JP-A-7-114251 (JP, A) JP-A-6-342237 (JP, A) JP-A-58-81538 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/02

Claims (4)

(57) [Claims] 1. A charging roller, which is disposed in contact with a driving rotating endless photoreceptor and rotates following the drum, and a cleaning roller member that contacts the charging surface of the charging roller and cleans the charging surface. in the charging device consisting comprises, together constituting the cleaning roller member with a sponge-like elastic roller, in a direction in which the forward feed rotation at the contact position between the charging roller, the sponge-like elastic low
La is rotationally driven, spongy bullet in said contact position
The peripheral speed of the sex rollers sets the rotational speed of the sponge-like elastic roller so as to be larger than the peripheral speed of the charging roller due to the driving of the photosensitive member, the sponge-like elastic roller and the charging roller to the spacing between them is constant It is controlled to be further charging roller shaft, movable and biases the pressure toward the photosensitive drum axis center, thereby between the charging roller and the dynamic friction coefficient between the sponge-like elastic roller and the charging roller photosensitive drum A charging coefficient set to be smaller than the dynamic friction coefficient of the charging device. 2. A charging roller, which is disposed in contact with a driving rotating endless photosensitive member and rotates following the drum, and cleans the charging surface by contacting the charging surface of the charging roller.
In the charging device comprising comprising a cleaning roller member, the cleaning roller member with constituting a sponge-like elastic roller, in a direction in which the forward feed rotation at the contact position between the charging roller, the sponge-like elastic low
La is rotationally driven, spongy bullet in said contact position
The peripheral speed of the sex rollers sets the rotational speed of the sponge-like elastic roller so as to be larger than the peripheral speed of the charging roller due to the driving of the photosensitive member, the dynamic friction coefficient between the charging roller and the sponge-like elastic roller and the charging roller The coefficient of kinetic friction between the photosensitive drums is set to be smaller than that of the photosensitive drum, and the surface of the cleaning roller member composed of the sponge-like elastic roller is shaped by a grinding wheel or the like while microscopically shaving the surface. A charging device characterized in that brush-like micro pieces protrude from a surface layer. 3. A photoreceptor which is driven and rotated and is arranged in contact with the photoreceptor.
A charging roller that contacts the charging surface of the charging roller and
A sponge-like roller member for cleaning the surfacePrepare
Image forming apparatus,At the contact position with the charging roller
In the direction of forward feed rotation,Sponge-like
Roller memberIs driven to rotate, and further at the contact position.
SaidSponge roller memberThe peripheral speed of the charging roller.
To be greater than speedSponge roller memberRotation speed
Set and rotate the charging roller with respect to the photoconductor.Let  SaidSponge roller memberThe diameter of the charging roller
Slightly larger than the diameter,Sponge roller memberThe cell
The number of sponge material is about 10-60 pieces / inch.
The OPC photosensitive drum has a rubber layer on the surface of the charging roller.
When the hardness of the rubber layer on the surface side is 30 to 30 as measured by Asker-C.
Each is configured to be 50 degrees, and the charging roller
WhenSponge roller memberDynamic friction coefficient between the charging roller and
It is noted that the coefficient is set smaller than the dynamic friction coefficient between the photosensitive drums.
An image forming apparatus. 4. An image forming apparatus comprising: a charging roller arranged in contact with a photosensitive member that is driven and rotated; and a cleaning roller member that contacts a charged surface of the charging roller to clean the charged surface. the charging roller is driven to rotate the photosensitive member, whereas with configuring the cleaning roller member with a sponge-like elastic roller, in a direction in which the forward feed rotation at the contact position between the charging roller, the sponge-like elastic
The roller is driven and rotated, and the sponge at the contact position is rotated.
The rotational speed of the sponge-like elastic roller is set so that the peripheral speed of the elastic roller is greater than the peripheral speed of the charging roller. Further, the dynamic friction coefficient between the charging roller and the sponge-like elastic roller is set between the charging roller and the photosensitive drum. The coefficient of kinetic friction is set to be smaller, and the surface of the cleaning roller member composed of the sponge-like elastic roller is shaped by a grinding wheel or the like while microscopically shaving the surface, and the surface is brushed from the surface layer of a sharp skeleton. An image forming apparatus, wherein minute pieces are projected.